Allow prioritizing specific groupIds, resolves Ekryd/sortpom#504

[pwoodworth]

Adding two mojo parameters:

• priorityGroupIds -- Comma-separated ordered list of group ids to prioritize in sorting.
• prioritizeProjectGroupId (Default: false) -- Whether to add the project group id to the priorityGroupIds list.

These parameters affect the sorting of both dependencies and plugins.

[pwoodworth]

I'm guessing the security/snyk failure is due to the addition of the maven-core dependency, but since it has provided scope I'd argue it isn't really an issue. That said, I could move the prioritizeProjectGroupId option (along with the added maven-core dependency) to a followup PR if that would be preferable.